Power injector for injecting fluid into animals

ABSTRACT

An animal fluid injector is provided with a syringe guide, preferably in the form of a pressure jacket, having an open front end through which a replaceable disposable syringe is loadable into and unloadable from, thereby permitting replacement without retraction of the syringe plunger drive or disconnection of the injection tubing. The injector is provided with structure, preferably in the form of thread sections, which mates with cooperating structure on the syringe, to connect and lock the syringe to the injector, preferably by rotational motion of, preferably, less than a full turn, of for example, 90°. In the illustrated embodiment, the structure is at the front end of the guide or at the front periphery of a jacket to connect to threads on a pressure restraining front end of the syringe. A mechanism in the injector, which includes, for example, a key on cam ring provided with a lever that is preferably manually operable with one hand of an operator, interacts with structure such asymmetrically spaced notches on the back end of the syringe to, for example, rotate the syringe and simultaneously translate or rotate a coupling on the syringe plunger into and out of engagement with jaws provided of a plunger drive in the injector.

This is a divisional of U.S. patent application Ser. No. 07/712,110,filed Jun. 7, 1991, now U.S. Pat. No. 5,300,031. This application isrelated to, and is also a divisional of U.S. patent application Ser. No.08/158,765, filed Nov. 30, 1993, which is copending and is a divisionalof U.S. patent application Ser. No. 07/881,782, filed May 11, 1992, nowU.S. Pat. No. 5,279,569, which is also a divisional of U.S. patentapplication Ser. No. 07/712,110 referred to above.

The present invention relates to injectors and more particularly todisposable replacement syringes for animal fluid injectors.

BACKGROUND OF THE INVENTION

Injectors are devices that expel fluid, such as contrasting media, froma syringe and through a tube into an animal. The injectors are providedwith an injector unit, usually adjustably fixed to a stand or support,having a drive that couples to the plunger of the syringe to drive itforward to expel fluid into the tube, or that may be driven rearward todraw fluid into the syringe to fill it. Usually the syringe is adisposable replacement type.

In the injection phase where the plunger is driven forward, pressuresare developed in the syringe that range from, for example, twenty-fivepsi for some applications to over 1000 to 1200 psi for otherapplications. Syringes that will contain fluid under such pressures areexpensive and therefore impractical where the syringes are to bedisposable. Accordingly, many such injectors, such as angiographicinjectors, for example, have been provided with pressure jackets fixedto the injector units and into which the syringes are inserted. Thepressure jackets contact the outer surfaces of the syringe to restrainthe walls of the syringe against the internal pressures.

To hold the syringes in the pressure jackets, the jackets of the priorart have been configured to surround the front ends of the syringes torestrain the syringe front wall against forward acting forces of thedrive and the fluid pressure and to hold the syringe in the jacket.Because the front end of the pressure jacket is closed, rear loading wasnecessary, and accessibility thereto was provided by hinging or rotatingthe jacket to allow for removal and replacement of the syringe from therear. The opening and reclosing of the injector unit to replace thesyringe requires a certain amount of time, which, in the course of theprocedure being performed, is not wholly desirable.

Furthermore, while for many years injector units of various types havebeen capable of disconnection of the plunger drive from the drivecoupling on the syringe plunger at any position of the plunger withinthe syringe, retraction of the drive is typically required before thesyringe can be removed. This is because the opening of the injector unitto remove and insert the syringe from the rear requires, for example, atranslating or rotating of the jacket from the axis of the drive, whichcannot be achieved if the plunger drive is extended.

For example, at the end of an injection procedure, the syringe plungertypically is forward, as is the plunger drive. Since, in the prior artinjectors that load from the rear, the pressure jacket is moved throughthe position that the drive occupies when extended in order to removethe syringe. Hence, the syringe cannot be immediately removed withoutretracting the plunger drive. Further, the disposable tubing thatconnects to the nozzle of the syringe must be disconnected from thesyringe in order to remove the syringe from the jacket. Additionally,when an empty new syringe is inserted, the drive must be in itsretracted position.

More often than not, the syringe is inserted empty and filled byretraction of the plunger with an injection tube connected to a supplyof the fluid that is to be injected. In addition, before an empty newsyringe can be filled, it is necessary that the plunger be fully forwardin the syringe so that the syringe can be filled by rearward retractionof the plunger. As a consequence of the need with such prior artinjectors to retract the drive upon loading the syringe, it is thennecessary to fully advance the drive to the position in which it inengagement with the plunger and the plunger is in its full forwardposition. The drive then engages a coupling on the plunger of thereplacement syringe. This need to retract and advance the drivecontributes to a loss of time in the syringe replacement process.

Accordingly, there has been a need to more quickly load and unloaddisposable replacement syringes in angiographic injectors, and forinjectors and replacement syringes that can accommodate a more efficientprocess of syringe replacement.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a method andapparatus by which replaceable syringes can be more efficiently loadedinto and unloaded from injectors.

It is a more particular objective of the present invention to provide aninjector, more particularly an angiographic injector, a replacementsyringe therefor, and a method of replacing the syringe in the injectorthat provide for more efficient replacement of the syringes in theinjector. It is an additional objective of the present invention toprovide an injector wherein a used syringe can be removed and a new oneinserted in the injector without retraction of the drive from thepressure jacket, in most applications. It is a further objective of theinvention to allow for the removal of the used syringe from the jacketwithout disconnection of the injector tube from the syringe nozzle.

It is still a further objective of the present invention to provide aninjector, replaceable syringe and method of syringe replacement withwhich the replacement of the syringe can be achieved with simple motionsby the operator or with rapid operation of injector unit mechanisms.

An additional objective of the present invention is to provide aninjector and replaceable syringe therefor that will facilitate controlof the orientation of the syringe in the jacket, and thereby provide forpositive, rapid and reliable engagement of the syringe with lockingstructure that holds the syringe in the jacket, engagement of theplunger drive and plunger drive coupling, or connection of the injectiontube to the outlet of the syringe.

A further objective of the present invention is to provide for easy tooperate mechanism and reliable locking structure for locking the syringein place in the pressure jacket of the injection unit.

Another objective of the present invention is to provide an injector andsyringe arrangement that minimizes or eliminates the probability ofspillage from the syringe nozzle flowing into the injector equipment,and otherwise enhancing the ability to maintain sterility andcleanliness 10 of the equipment.

According to the principles of the present invention, there is providedan angiographic injector having a front end loadable syringe that can beloaded into and removed from the injector pressure jacket through anopening that is provided in the front end of the pressure jacket. Toprovide this front end loadable feature, the syringes of the preferredand illustrated embodiments of the present invention are provided with afront wall that is pressure restraining, that is, is of sufficientstrength to support the front of the syringe against the expectedpressures within the syringe, and that is securable to the front end ofthe pressure jacket so as to complete the pressure restraining enclosureof the syringe within the pressure jacket and hold the syringe in thejacket. In one preferred form, this front end of the injector is formedof a separate pressure restraining cap made of material that is separatefrom the front wall of the syringe and may be reusable. In anotherpreferred form, the cap may be formed integrally of the front syringewall. With the cooperating structure of the jacket and the syringe,restraining of the pressure jacket along the front and sides of thesyringe is provided where the jacket allows for the replacement of thesyringe from the front.

In one preferred and illustrated embodiment of the invention, the frontend of the syringe locks to the front end of the pressure jacket througha cooperating engagement of mating threads on the syringe jacket. Thethreads include external thread sections formed at the front end of thepressure jacket and internal threads formed on an outwardly extendingflange or rim of the front wall of the syringe, preferable on a pressurerestraining cap. Alternatively, other securing or locking structure suchas a clip or an adaptor, for example, may be employed to join thesyringe to the jacket.

In the preferred embodiment of the present invention, the threads areengageable in a limited number of angular positions to therebypredetermine the angular orientation of the syringe in the pressurejacket. Additionally, other keys and keyways carried respectively by theunit and by the syringe limit the angular position in which the syringemay be inserted into the jacket to a unique predetermined angularorientation. Preferably, three keyways, such as slots or notches,unequally spaced around the back, rearward or proximate edge of thesyringe body, engage similarly spaced keys or tabs on the unit at therear end of the pressure jacket to permit insertion of the syringe intothe jacket in one and only one orientation.

Further in accordance with principles of the present invention, in itspreferred embodiment, a coupling on the syringe plunger is centrallylocated and symmetrical about the axis of the plunger. A pair of jaws onthe plunger drive is moveable either by transverse straight or arcuatetranslatory motion or by forward longitudinal motion to form aconnection between the coupling and the drive. Once coupled to thedrive, the coupling remains engaged to the drive during longitudinalmotion of the drive to cause the plunger to move forward or backwardwith the drive. Disengagement occurs thereafter only upon transversetranslational motion of the plunger with respect to the drive. Incertain embodiments, this translatory transverse motion occurs bytranslatory movement of the jacket, and the injector unit door thatcarries the jacket, with respect to the plunger drive and the unithousing. In other embodiments, an asymmetrical coupling is provided thatengages and disengages the plunger drive upon rotational movement of thesyringe with respect to the drive.

Preferably, the motion for locking the syringe to, and unlocking thesyringe from, the jacket is achieved by rotation of the syringe in thejacket, and preferably, this motion is linked to, and occurssimultaneous with, the motion that engages and disengages the plungercoupling and drive, whether that coupling is by translation or rotation.In addition, the syringe and plunger drive are so dimensioned andpositioned to prevent contact between the drive and the sterile interiorwall of the syringe, regardless of the position of the drive, as thesyringe is being loaded.

Preferably, the syringe is formed of a cylindrical body, with the frontend in the shape of a truncated cone that terminates in a forwardlyextending neck with an orifice at its remote end that is connectablewith an injection tube. The front end of the syringe is shaped so as todirect fluid leaking from the nozzle outwardly around the front end ofthe jacket. This prevents leakage, which often results upondisconnection of the injection tubing, from entering the space betweenthe pressure jacket and the syringe body.

Replacement of the syringe begins, in the preferred embodiments of theinvention, with the unlocking the syringe at its front end from thefront end of the pressure jacket, preferably by rotating the syringewith respect to the jacket, and by disengaging the plunger drive fromthe syringe plunger, alternatively by transverse translational orrotational motion, preferably simultaneous with and linked to the motionthat disengages the syringe from the jacket. The unlocking of thesyringe from the jacket occurs, for example, by loosening mating threadsat the front of the syringe and jacket. The twisting of the syringe inthe jacket is linked to motion that either translates transversely orrotates a coupling on the syringe plunger out of engagement with theplunger drive.

Then the syringe is removed from the jacket through the open front endof the jacket. This removal may take place without retraction of theplunger drive, should the drive be advanced in the pressure jacket atthe time of disengagement from the plunger coupling. The used syringemay also be removed without disconnection of the disposable injectiontubing from the nozzle of the syringe.

When the used syringe is removed, a replacement syringe is inserted intothe jacket through its open forward end and the front end of the newsyringe is locked to the front end of the jacket, preferably by relativerotation of the syringe in the jacket to cause, for example, engagementbetween mating threads on the front end of the syringe and the front endof the jacket. The plunger drive, in one embodiment, is translated tobring the plunger coupling engaging jaws into alignment with the plungercoupling, preferably simultaneously with the locking of the syringe tothe jacket. The jaws thereby either engage the coupling upon thetranslatory motion, or thereafter engage the coupling by longitudinaladvancement of the drive against the coupling. In one embodiment, thejaws are positioned off center of the drive so that the drive, whetherin the engaging or the disengaging positions, does not contact a syringeas the syringe is guided by the jacket during loading.

In an alternative embodiment, engagement of the plunger drive with thecoupling occurs by relative rotation of the drive and the coupling,preferably by rotating the coupling relative to a stationary plungerdrive, rather than by translational motion between the drive and thecoupling. Only if the rest position of the plunger of the replacementsyringe is behind the final position of the plunger drive at the time itwas disconnected from the coupling of the plunger of the syringe beingreplaced need the plunger drive be retracted.

The engagement and disengagement motions between the plunger drive andplunger drive coupling, and between the syringe and the pressure jacket,are provided with manually operable mechanism that, in the preferred andillustrated embodiments, rotates the syringe in the jacket and furthereither rotates or translates the coupling with respect to the plungerdrive, with a simple one hand operated mechanism. The mechanism providesa convenient lever, operable through a short arc, to rotate the syringein the jacket and to then, preferably, translate the pressure jacketthat carries the syringe and is carried by the injector unit door, or tootherwise move the syringe with respect to the drive, to bring theplunger coupling of the syringe into or out of alignment with theplunger drive.

The present invention provides a disposable syringe that may be replacedin an angiographic or CT injector with great efficiency and speed.Further, replacement may occur without retraction of the plunger driveof the injector unit. Simple and rapid one hand operation of theengaging and disengaging structure is provided.

These and other objectives of the present invention will be more readilyapparent from the following detailed description of the drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an angiographic CT injector embodyingprinciples of the present invention.

FIG. 1A is a perspective view of an another form of angiographicinjector embodying principles of the present invention.

FIG. 2 is an exploded perspective view of a portion of one preferredembodiment of the injector of FIG. 1.

FIG. 3 is a perspective view of the portion of the injector of FIG. 2.

FIG. 4 is a cross-sectional view along lines 4--4 of FIG. 3 illustratinga replaceable syringe unlocked from the housing for insertion into orremoval therefrom.

FIG. 5 is a cross-sectional view similar to FIG. 4 but illustrating thesyringe locked to the structure carried by the housing.

FIG. 6 is a cross-sectional view along the line 6--6 of FIG. 5.

FIG. 7 is an elevational diagrammatic illustration of the injector ofFIG. 1 with the pressure jacket and syringe removed, and showing thesyringe locking structure in the locked position such as in FIGS. 5 and6.

FIG. 8 is an elevational diagrammatic view similar to FIG. 7illustrating the syringe locking structure in the unlocked position suchas in FIGS. 2-4.

FIG. 9 is an elevational diagrammatic view similar to FIG. 7illustrating the locking mechanism in the housing door release position.

FIG. 10 is a cross-sectional view through the housing of the injectortaken along lines 10--10 of FIG. 1 with the plunger drive disengagedfrom the syringe plunger coupling.

FIG. 11 is a view of a portion of FIG. 10 illustrating the plunger drivelongitudinally moving into engagement with the plunger coupling.

FIG. 12 is a view of a portion of FIG. 10 illustrating the plunger drivein engagement with the plunger coupling.

FIG. 13 is a front view of a portion of another embodiment of theinjector of FIG. 1.

FIG. 14 is a view of an alternative embodiment of a portion of a syringeaccording to principles of the present invention.

FIG. 15 is a cross-sectional view similar to FIG. 5 of an alternativeembodiment of the invention, illustrating alternative engaging structurebetween the front ends of the syringe and jacket.

FIG. 16 is a cross-sectional view similar-to FIG. 5 of a furtheralternative embodiment of the invention, also illustrating alternativeengaging structure between the front ends of the syringe and jacket.

FIG. 17 is a front end view of still a further alternative embodiment ofthe invention, also illustrating alternative engaging structure betweenthe front ends of the syringe and jacket.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, an angiographic injector 10 according to anotherpreferred embodiment of the present invention is illustrated, configuredfor CT applications. The injector 10 includes a ceiling mounted support11, adjacent a CT X-ray unit, to the lower surface of which is rigidlysupported a vertically descending support column 12.

Remote from the support 11 is an injector control module console 13behind a wall which isolates the operator area from the X-ray equipment.The console 13 is located adjacent a control 14 of the X-ray equipment.Electrical power and control cables (not shown) communicate power andcontrol signals through the support 11 and the column 12 and to a powerlead 15. The console 13 connects with an injector control module 16,which includes a programmable microprocessor (not shown) to whichcommands and programming codes are input through a keyboard 17 on theconsole 13. The console 13 is also provided with an operator display 18to aid in interfacing the input commands and injector status with theoperator.

Attached to the column 12 is an articulating adjustable arm 19. To theremote end of the arm 19 is adjustably supported injection module unit20. The arm 19 is capable of setting the unit 20 at varying positionsadjacent a patient bed of the CT unit.

Referring to FIG. 1A, an angiographic injector 10a according to anotherpreferred embodiment of the present invention is illustrated. Theinjector 10a includes a wheeled base 11a to the top of which is rigidlysupported a vertically adjustable upstanding support column 12a. To thetop of the column 12a is supported a control module platform 13a.Electrical power is communicated from a power cord (not shown) throughthe base 11 and the upstanding support 12a and through a power lead 15ato a control module 16a rigidly supported to the platform 13a. Thecontrol module 16a includes a programmable microprocessor (not shown) towhich commands and programming codes are input through a keyboard 17a onthe module 16a. The module 16a is also provided with an operator display18a to aid in interfacing the input commands and injector status withthe operator. Attached to the platform 13a is an articulating adjustablearm 19a. To the remote end of the arm 19a is adjustably supported theinjection module unit 20.

The injection module unit 20 of the embodiments of FIGS. 1 and 1Aincludes a housing 21 which contains the operating drive structure ofthe injector 10 or 10a. The housing 21 has a support bracket 23 fixedthereto and adjustably pivotally supported to the remote end 24 of thearticulating arm 19 or 19a. The housing 21 has pivotally attached to thefront thereof a door 25 at the front thereof which is pivotallyconnected to the housing 21 at a longitudinally extending pivot or hingepin 26 (FIG. 2) rigidly supported on the housing 21 and extendingforwardly from the front of the housing 21.

On the top of the housing 21 is an injector position and local controlpanel 27 having a position indicator scale 28 thereon, which displaysthe position of the injector drive to the operator. The panel 27 alsoincludes a pair of forward and reverse drive direction control buttons29, which are selectively actuatable to activate a drive within thehousing 21 in either the forward or reverse directions.

Extending forwardly from the front of the door 25 is an injector syringeand pressure jacket assembly 30, the structure of which can be betterunderstood with reference to FIGS. 2-5 below. The syringe and jacketassembly 30 includes a hard plastic pressure jacket 31, which may be ofopaque or transparent material, a removable and replaceable disposablesyringe 32, which may be of opaque, transparent or semi-transparentmaterial, and related structure hereinafter described.

The syringe 32 is disposable, and includes walls which will withstandonly moderate or low pressure. The walls are usually outwardlydeformable under operating pressures, particularly pressures of 300 psior more. Such higher pressures are necessary to overcome pressure dropsthrough the injection tubing at higher flow rates, which are oftendesirable. The jacket 31 is made of a stronger transparent material thatwill withstand the operating pressures. When the syringe 32 is containedin the jacket 31, it is surrounded by the jacket 31 and supported by thejacket 31 against expansion caused by the fluid pressure within as thesyringe 32 expands against the jacket wall.

The pressure jacket 31 has a generally cylindrical inner bore 33extending therethrough from a proximate end 34 adjacent the door 25 to aremote end 35 of the pressure jacket 31 toward the front of the unit 20.The bore 33 is dimensioned so as to receive through the remote end 35the disposable syringe 32 and to support the syringe against expansionfrom fluid pressure within such fluid pressure may range to more than athousand psi. The pressure jacket 31 has an annular flange 37 extendingoutwardly around the proximate end 34. The flange 37 is integrallyformed with the jacket cylinder and is shaped to conform to an annularrecess 38 surrounding a circular hole 39 in the door 25 to which thejacket 31 may be assembled by insertion from the rear. The hole oropening 39 in the door 25 and the cylindrical bore 33 of the jacket 31are concentric with a longitudinal axis 40 on which also lies an axis 41of the syringe 32 when the syringe 32 is positioned in the bore 33 ofthe jacket 31. The jacket 31 is firmly and rigidly attached to the door25 with a pair of screws 43, only one of which is shown, which arethreaded into a pair of holes 44 in the back of the door 25 (FIG. 2). AnO-ring seal 46 surrounds the flange 37 of the jacket 31 in the recess 38of the door 25.

The syringe 32 includes a syringe case 50 formed of a single piece ofmolded plastic material, a pressure cap 51, a tubing collar 52 (FIG. 3)and a plunger 54 (FIGS. 3-5). The syringe case 50 includes a cylindricalsyringe body 55 having an open proximate end 56 and a remote end 58 towhich is integrally formed a conical front wall 57. The front wall 57 istruncated at its forward end, to which is integrally formed an elongatedneck 59 extending from the wall 57 at the center thereof. The neck 59 ofthe syringe case 50 has an orifice 60 (FIG. 3) in its remote end whichcommunicates with an internal syringe cavity 61 formed within the neck59, the conical front wall 57 and the cylindrical body 55 of the case 50of the syringe 32. The rear end of the cavity 61 is further defined by aforward facing conical surface 64 of the plunger 54. The conical surface64 is of a slope which conforms to the slope of the interior of theconical front wall 57. The plunger 54 is slidable within the body 55 ofthe syringe case 50 such that the cavity 61 is of variable volume.

Near the front end of the neck 59 of the syringe case 50, just behindthe orifice 60, is an external thread 66 configured to mate with threads67 on the interior of collar 52 (FIG. 3). The thread 66 in the neck 59has an stop 69 at near forward end thereof to engage an abrupt step 70on the thread 67 of the collar 52 so that, when the syringe 32 isproperly oriented in the jacket the collar 52, when loosened to itsmaximum extent, will assume a predetermined orientation so as topresent, in an upwardly facing orientation, a tube end receiving slot 62formed in the remote end of the collar 52. This slot 62 is of T-shapedcross-section so as to receive the enlarged flange end 63 of a tube 65through which fluid from the syringe cavity 61 is injected into apatient.

The cap 51 is generally conical in shape and has an inner rearwardsurface 75, which conforms to the front surface of the conical wall 57of the case 50 of the syringe 32. In certain embodiments, the rearwardconical surface 75 of the cap 51 may be bonded to the front surface ofthe conical wall 57 of the case 50 of the syringe 32, or it may beformed integrally therewith, molded from the same plastic material asthe case 50 of the syringe 32. In the preferred and illustratedembodiment, the cap 51 is separate from the syringe body portion 55 andhas a pair of holes or detents 76 into which fit a pair of projections77 extending forwardly from and formed integrally on the outer surfaceof the conical wall 57 of the case 50 of the syringe 32. The cooperationof the pins or projections 77 with the holes or detents 76 prevent thecap from rotating with respect to the syringe case 50 when the cap 51 ismounted on the syringe 32.

To hold the cap 51 against the conical wall 57 of the case 50 of thesyringe 32, six resilient tabs 78 are formed about a central inner hole79 of the cap 51. The tabs 78 are separated by six equally spaced radialslots 80 (FIG. 3). The hole 79 in the cap 51 is equal to or onlyslightly greater in size than the circular forward end of the conicalwall 57 of the case 50 of the syringe 32. The neck 59 of the syringe 32has an enlarged straight section 81 slightly greater in diameter thanthe hole 79 in the cap 51 and also greater in diameter than the forwardend of the conical wall 57 of the case 50, thereby forming a groove 82at the juncture of the straight neck portion 81 with the conical wall 57so that the tips of the tabs 78, which are sufficiently resilient toslide over the enlarged neck portion 81 as the cap 51 is inserted on thecase 50 of the syringe 32 with the hole 79 surrounding the neck 59 tosnap fit into the groove 82.

The syringe 32 includes structure that is configured to lock the syringe32 to the front end of the jacket 31 by cooperating with matingstructure on the jacket 31. The jacket 31 has, spaced around thecircumference thereof near the remote or front end 35 of the jacket 31,four equally spaced outwardly projecting thread sections 85. Thesethread sections 85 are slightly less than 45° in extension around thecircumference of the jacket 31 and are spaced apart with gaps ofslightly greater than 45°. The cap 51 has a cylindrical rim 87 in whichare formed four similarly sized and spaced mating thread sections 86.The thread sections 86 project inwardly toward the jacket 31 when thesyringe 32 is positioned in the jacket 31. As such, when the syringe 32,with the cap 51 assembled to it is inserted into the jacket 31, thethreads 86 of the cap 51 pass through the spaces between the threads 85on the jacket 31 to a point behind the threads 85. When so inserted, thesyringe assembly 32 with the cap 51 may be twisted clockwise 45° totighten and thereby secure the cap 51 to the jacket 31 by engagementbetween the threads 85 and 86 as shown in FIG. 5, to thereby lock thesyringe in the bore

The piston 54 of the syringe 32 is molded of an elastomeric material.Preferably, the piston 54 includes two portions molded of differentmaterials and bonded together. These portions include a forward moreflexible portion 90 in which is formed the forward conical surface 34.This forward portion 90 has a pair of outwardly extending rings 91formed in the periphery thereof to make sealing engagement with theinside of the wall of the cylindrical body 55 of the syringe case 50.The rearward portion of the piston 54 is a flat circular surface towhich is bonded the flat circular forward surface of a more rigid rearportion 93 of the piston 54. The rear rigid portion 93 of the piston 54is molded of a harder stronger plastic material and has a rearwardfacing circular surface 95 having a rearward extending coupling 96integrally formed thereon at its center. The coupling 96 includes arearwardly extending cylindrical shaft 97 on the axis 41 of the syringe32 and a larger symmetrical cylindrical button 98 integrally formed atthe rear end of the cylindrical shaft 97.

Referring to FIG. 10, a piston drive assembly 100 is illustratedcontained within the housing 21. The drive assembly 100 includes anelectric motor 101 mounted within the fixed housing 21 and having arotary output shaft 102 with a drive gear 103 fixed to the remote endthereof. The drive gear 103 is positioned for driving engagement with adriven gear 104 fixed near the rear end of a drive screw or shaft 105supported at its rear end in a bearing 106 fixed in the housing 21. Thescrew or shaft 105 has a continuous external helical thread 107 thereonwhich mates with interior threads of a carriage 108. The carriage 108 isslidably supported in a bushing 109 fixed in the housing 21. The shaft105 rotates within the housing 21 about a longitudinal axis 112.

At the forward end of the carriage 108 is supported a pair of hookedjaws 114 which are pivotally mounted at their rearward ends by a pair ofpivot pins 115 to the carriage 108. The jaws 114 are biased toward theaxis 112 by a pair of balls 116a and 116b of resilient materialpositioned between the outside of the jaws 114 and an inner cylindricalwall 117 of a recess 118 formed in the forward end of the carriage 108.The balls 116a, 116b are partially captured in depressions in the outersurfaces of the jaws 114. The balls 116a, 116b bias the jaws towardtheir innermost position toward the axis 112. The innermost position ofthe jaws is determined by a spacing block 119 on the axis 112 of thecarriage 108 at the center of the cavity 118.

When a syringe 32 is locked in the jacket 31 with its axis 41 and theaxis 40 of the jacket 31 may be in alignment with the axis 112 of theshaft 105, the plunger 54 may be located in the cylindrical body 55 ofthe syringe case 50 in a position forward of the remote end 56.Preferably, however, the jaws 114 are displaced to the side of axis 112of the shaft 105 so that as the jaws 114 and coupling tip 98 are intheir disengagement position, maximum clearance is provided so that thesyringe 32 may be inserted into the jacket 31 without the sterileinternal walls of the syringe 31 touching the components of the drive,as illustrated in the figures.

In the engaging position, the jaws 114 are nonetheless in alignment withthe coupling 98 on the axes 40 and 41 of the jacket 32 and syringe 32.In such a situation, the jaws 114 may be in a retracted position at thecenter of the opening 39 of the door 25 adjacent to the proximate end 34of the jacket 31, and out of engagement with the coupling 96 on theplunger 54. From this position, operation of the motor 101 rotates theshaft 105 and drives the carriage 108 forwardly to move the jaws 114toward and into engagement with the coupling 96 on the plunger 54. Thisengagement takes place as shown in FIG. 11 where a pair of tapered camsurfaces 120 at the forward interface of the tips of the jaws 114 engagethe enlarged portion or button 98 of the coupling 96 to expand the jaws,as shown in FIG. 11, to snap around the button 98 of the coupling 96 toform a driving engagement between the drive assembly 100 and thecoupling 96 of the plunger 54 as shown in FIG. 12. Once so engaged, anyforward or reverse movement of the carriage 108 under the power of themotor 101 will cause the plunger 54 to be driven either forwardly orbackwardly in the syringe body 55.

Disengagement of the jaws 114 from the coupling 96 can thereafter beachieved by translational movement between the coupling 96 and the jaws114 between a disengaged position as shown in FIG. 4 and an engagedposition as shown in FIG. 5. When the plunger coupling 96 and the jaws114 are disengaged, the syringe 32 can be replaced without the need toretract the carriage 108 of the drive 100. This allows for rapidreplacement of the syringe 32. Preferably, the jaws 114 are either fullyretracted toward the housing 21 where engagement by translation of thecoupling 96 will occur, or the jaws 114 are sufficiently within thejacket prior to replacement of the syringe so that the coupling 96 ofthe replacement syringe 32 will not contact the jaws 114 except as thedrive 100 is advanced.

If sterility is not a problem, the most time saving approach would be toinsert the syringe 32 into the jacket 31 with its plunger all the wayforward and the drive fully advanced so that, when the syringe istranslated toward the jaws 114, engagement will immediately occur andthe plunger can be immediately retracted to fill the syringe.

When a syringe 32 is inserted into the jacket 31 when the plunger 54 isat its rearmost position toward the proximate end 56 of the syringe body55, the coupling 96 is in a position adjacent the proximate end 56 ofthe syringe body 55 and projecting rearwardly therebeyond. When in sucha position, engagement between the jaws 114 and the coupling 96 isbrought about by translational movement between the position shown inFIG. 4 and that shown in FIG. 5. In the unlocked or disengaged positionshown in FIG. 4, the axes 40 and 41 of the jacket 31 and the syringe 32,respectively, as well as the center of the opening 39 of the door 25,lie spaced from and parallel to the axis 112 of the shaft 105 as shownin FIG. 4. In the locked or engaged position, the axis 112 of the shaft105 is slightly eccentric relative to the axes 40 and 41 of the jacket31 and syringe 32, respectively, as shown in FIG. 5. This translationalmovement, the engagement and disengagement between the coupling 96 andthe jaws 114 and the 45° rotational movement which secures the cap 51 tothe pressure jacket 31 by engagement of the threads 85 and 86 arebrought about by operation of a translating and locking mechanism 125,which is best understood by reference to FIGS. 2-9.

The translating and locking mechanism 125 includes a cam and lockingring 127 which is rotatably retained in a circular recess 126 in theback of the door 25. The ring 127 has a generally semi-circular groove130 in the back surface thereof for receiving a spring wire retainingclip 131 having a pair of looped ends 133 which extend through a pair ofslots 134 in the rim of the ring 127 and into a selected one of threepair of diametrically opposed notches 135, 136 and 137 in the inner wallof the rim of the recess 126 in the door 25. The three pair of notches135, 136 and 137 represent three positions of the translating andlocking mechanism 125 which are the locked, unlocked and releasepositions, respectively. The locked position of the mechanism 125 inwhich the loops 133 of the ring 131 are in the notches 135, is thatillustrated in FIGS. 5-7 and 10. The unlocked position, in which theloops 133 of the ring 1.31 are in the notches 136, is that illustratedin FIGS. 2-4 and 8. The release position, in which the loops 135 of theclip 133 are in notches 137, is that illustrated in FIG. 9. The ring 127is moved among these three positions by a manually accessible handle 138in the form of a cylindrical knob 139 rotatably attached to a lever arm140 formed integrally and extending radially from the ring 127 through aslot 141 in the door 25 (FIG. 1). The ring 127 is retained in the recess126 by a pair of screws 143 which thread into countersunk holes 144 atthe periphery of the recess 126 in the back of the door 25. These screws143 have enlarged heads 146, which, when seated in the holes 144,overlie the edge of the ring 127, thereby securing it for rotatablemovement within the recess 126.

As shown in FIGS. 2 and 6, the ring 127 has an inner periphery 149 whichis larger than the circumference of the body 55 of the syringe case 50.Accordingly, when the syringe 32 is inserted in the jacket 31, theproximate end 56 of the syringe case 50 extends through and issurrounded by the inner periphery 149 of the ring 127. Asymmetric keywaystructure, preferably in the form of three slots or notches 151, 152 and153 (FIG. 6) are provided in the edge of the proximate end 56 of thebody 55 of the syringe case 50. The spacings between adjacent pairs ofthe notches 151-153 differ from each other. Formed integrally of thering 127 and projecting inwardly from the inner periphery 149 thereofare three tabs or keys 155, 156 and 157. These tabs 155-157 are spacedso as to fit into the respective notches 151-153 in the proximate end 56of the body 55 of the syringe case 50 so as to rotate the syringe 32 asthe mechanism 125 is rotated through actuation of the handle 138.Because the notches 151-153 and the tabs 155-157 are unequally spaced,they can only engage each other when the syringe 32 is inserted into thejacket 31 in one and only one orientation. That orientation is one whichwill cause the slot 62 of the collar 52 (FIG. 3) to align 45°counterclockwise of the vertical when the mechanism 125 is in itsunlocked position, which is a position in which it will be when thesyringe is first inserted into the jacket 31, and to be in an upwardlyfacing orientation, when fully loosened, when the mechanism 125 is movedto its locked position. Accordingly, the notches 135 and 136 in therecess 126, which receive the loops 133 of the spring clip 131 whenrespectively in the locked and unlocked positions, are 45° apart.

The rotation of the mechanism 125 from the unlocked position to thelocked position rotates the syringe 32 in the jacket 31 and rotates thecap such that its threads move from an unlocked position as shown inFIG. 4 to the locked position of FIG. 5, to secure the cap to the jacket31 by the engagement and tightening of the threads 85 and 86.

The translational movement of the axes 40 and 41 with respect to theaxis 112 is achieved by a fixed cylindrical cam follower or pin 150which projects outwardly from the fixed housing portion 22 behind thering 127 and into a cam slot 154 formed therein. The slot 154 is shapedso that the axes 40 and 41 which remain fixed with respect to the ring127, along with the door 25, the jacket 31, the syringe 32 and all ofthe structure mutually carried thereby, are moved in relation to theaxis 112 of the shaft 105 and the other structure mutually carried bythe housing 22, as the mechanism 125 is rotated. These axes move towardand away from each other in accordance with the shape of the slot 154determined by the radial distance from the point along the slot 154where it engages the pin 150 to the axes 40 and 41.

The cam slot 154 in the ring 127 is shaped such that, when the mechanism125 is in the locked position as shown, for example, in FIGS. 6 and 7,the distance between the pin 150 and the axes 40 and 41 is at a minimumand the axis 112 coincides with the axes 40 and 41. This is illustratedin FIGS. 5 and 7 wherein the coupling 96 is shown positioned between thejaws 114 and in mutual engagement therewith. When the mechanism 125 isin the unlocked position, with the loops 133 of clip 131 in the notches135 (FIG. 6) of the recess 126, the pin 150 lies in the slot 154 in theposition shown in FIG. 8, which is farther displaced from the axes 40and 41 than in the position of FIGS. 6 and 7, so that the coupling 96 istranslated to a position outside of the center line of the jaws 114, asshown in FIG. 8 and further illustrated in FIG. 4.

In the release position, as shown in FIG. 9, the pin 150 is positionedat the open end 160 of the cam surface of the slot 154 so that the door25 can be rotated upwardly about the hinge pin 26, as shown in FIG. 9,to open the space behind the door 25 for access thereto. This positionmay be used for cleaning the area behind the door 25 which is sometimesnecessary because of possible leakage of fluid from the cavity 61 intothe space behind the plunger 54. This can possibly occur because thefluid within the cavity 61, when being injected by forward advancementof the plunger 54, may be of relatively high pressure in the range,usually over 200 psi. For applications such as the injection ofcontrasting fluid for CT scanning, pressure may typically be in therange of from 25 to 300 psi., while in some angiographic injectionapplications the pressure may range to 1200 psi or higher.

In addition, leakage rearwardly along the exterior of the neck 59 of thesyringe 32 can cause fluid to flow between the body portion 55 of thesyringe 32 and the jacket 31. For this reason, the cap 51 is caused tofit snugly against the forward surface of the conical portion 57 of thesyringe 32 at least sufficiently to restrict the flow of this leakingfluid onto the neck 59. This is assisted by the configuration of the cap51 at the rim 87 thereof so as to divert away from the space between thesyringe 32 and jacket 31 fluid which might leak from the nozzle.

The front of the housing 21 has formed thereon a door stop 185 having aslot 186 formed therein for receiving a lug 187 of the door 25, torestrain the door 25 against forward force exerted by the drive 100.Behind the front of the housing 21 adjacent the stop 185 is a magneticsensor 188, which is responsive to the presence of a magnet 189 in thelever arm 139 of the handle 138. The sensor 188 generates a signal tothe control module 16 to activate the drive 100 only when the mechanism125 is in its locked position.

Referring to FIG. 13, there is illustrated a locking mechanism 225 thatis an alternative to the locking mechanism 125 described above. In thelocking mechanism 225, a stationary geared rack 250 is provided fixed tothe housing 21. A mating gear segment 254 is formed on the outer rim ofthe alternative locking ring 227 of this embodiment. The gear segment254 and rack 250 replace and function in the same way as the slot 154and pin 150 of the embodiment described above. As the mechanism 225 isrotated by the handle 138, the door 25 that carries the jacket 31 andthe syringe 32 is translated to bring the coupling 96 into or out ofengagement with the jaws 114 of the drive 100. Simultaneous with thistranslatory motion, the syringe 32 is rotated in the jacket 31 to lockor unlock the syringe 32 to the jacket 31 by engagement or disengagementof the threads 86 on the syringe 32 with the threads 85 on the jacket32.

FIG. 14 illustrates an alternative to the embodiment of the coupling 96described above. In the embodiment of FIG. 14, there is provided acoupling 296 that is T-shaped, having a rectangular endpiece 298 at therearward end of a cylindrical or square shaft 297 on the rearwardlyfacing circular surface 95 of the plunger 54. Such a coupling 296engages the jaws 114 by rotation of the locking mechanism 125 or 225,preferably through an angle of 90° When the orientation of the endpiece298 is parallel to the plane of the jaws 114, the drive 100 is locked tothe plunger 54 so that axial movement of the drive 100 moves the plungeraxially, in the forward direction to expel fluid form the syringe cavity61, or in a rearward direction to fill the cavity 61 with fluid. Whenthe endpiece 298 is perpendicular to the plane of the jaws 114, thecoupling 296 will move into or out of engagement with the jaws 114 uponrelative axial movement between the plunger 54 and the drive 100. Thus,with this embodiment, rotational motion, rather than translationalmotion, causes engagement and disengagement of the coupling 296 by thejaws 114. With this embodiment, orientation of the syringe 32, whenloaded into the jacket 31, is preferably maintained through thecooperation of the notches 151-153 and the tabs 154-156 (FIG. 4), sothat the coupling 296 will enter the jaws 114, when the syringe 32 isinserted into the jacket 31, with the endpiece 298 perpendicular to thepair of jaws 114.

The locking structure between the syringe 32 and the pressure jacket 31should provide for retention of the syringe 32 in the jacket 31 againstthe force of the fluid pressure in the cavity 61 or axial forceotherwise exerted on the plunger 54 by the drive 100. This locking ofthe syringe 32 to the jacket 31 is preferably achieved, as shown in FIG.5, by structure at or near the forward wall 57 of the syringe case 50.In accordance with the embodiment of FIG. 15, such structure may includeexternal threads 200 on the forward end of the syringe body 257, whichmate with internal threads 201 at the remote end of the jacket 31. Withsuch an embodiment, the syringe 32 is preferably provided with anannular flange 203 around the body 257 at the juncture of the body 257with the syringe front wall 258. The flange 203 inhibits the flow ofleaked fluid into the space between the syringe body 257 and the jacket31. With such an embodiment, the wall 258 is either thickened, providedwith reinforcing such as the ribs 208, or provided with other structureto resist deformation of the wall 258 under the pressure of the fluidwithin the cavity 61.

Alternatively, a reusable split clip 210 may be employed to secure acontinuous flange 203 of such a syringe to a continuous flange 212 atthe end of the pressure jacket in the embodiment of FIGS. 16. As afurther alternative as shown in FIG. 17, a ring clip 210a having anouter rim 215 and rotatably mounted to the syringe 31, encircles andengages outwardly projecting threads of a disk flange 213 formed at thefront end of the jacket 31, as the syringe 32 is twisted onto the jacket31, to engage the jacket in a manner similar to the threads 85 and 86 inthe embodiment of FIGS. 2-12 above.

The invention has been described in the context of its preferredembodiments. It will be appreciated by those skilled in the art thatvariations and alternatives to the embodiments described may be employedwithout departing from the principles of the present invention.Accordingly, this patent is not intended to be limited except by thescope of the following claims:

We claim:
 1. A front loadable power injector for injecting liquid intothe body of an animal from a disposable replacement syringe having afluid cavity therein, a front end discharge orifice communicating withthe cavity and a plunger moveable in the cavity and drivably accessiblefrom an open back of the syringe, the injector comprising:a housing; ahollow jacket extending forward from the housing and having an opensyringe-receiving front end; a drive ram movably supported on thehousing and having a front end axially extendable and retractabletherefrom within the jacket; a power unit carried by the housing anddrivably linked to the drive ram; a plunger coupling mounted on thefront end of the drive ram and operable to affect a connection betweenthe ram and the plunger of the syringe, when mounted in the jacket, uponrelative translatory motion between the ram and the plunger; linkageconnected between the ram and the jacket to impart relative translatorymotion therebetween; and a syringe lock carried by the jacket andoperable to lock a syringe to the jacket upon the rotational motion ofthe syringe relative to the jacket.
 2. The injector of claim 1wherein:the linkage is operative to impart the relative translatorymotion between the ram and the jacket in a direction transverse to thedirection of axial moveability of the ram within the jacket.
 3. Theinjector of claim 1 wherein:the linkage is disposed to operate upon therotational motion of the syringe relative to the jacket to impart therelative translatory motion between the ram and the jacketsimultaneously with the rotation of the syringe relative to the jacket.4. The injector of claim 1 further comprising:syringe-orientingstructure proximate the jacket operable to maintain a syringe receivedin the jacket in a predetermined angular orientation relative to thejacket.
 5. The injector of claim 1 wherein:the syringe lock includesthreads carried by the jacket and configured to form a locked connectionbetween the jacket and a syringe mounted in the jacket.
 6. A frontloadable injector for injecting fluid into the body of an animal from adisposable replacement syringe having a hollow body containing afillable fluid cavity on the interior thereof, a plunger axiallymoveable within the cavity, and a forward portion by which the syringecan be held for loading to and unloading from the injector, the injectorcomprising:a housing; a syringe guide carried by the housing having asyringe receiving front end; locking structure at least partiallycarried by the injector and configured to lock the syringe relative tothe injector while the forward portion of the syringe is being held; adrive ram movably supported on the housing and having a front endextendable and retractable therefrom in an axial path along the syringeguide; a power unit carried by the housing and drivably linked to thedrive ram; the syringe guide being configured relative to the path ofthe drive ram to maintain the interior of a syringe received by thesyringe guide out of contact with the ram when the ram is in an extendedposition along the path.
 7. The injector of claim 5 wherein:the syringeguide is substantially tubular and disposed concentric with the axialpath of the drive ram; and the syringe guide is configured to slidablyengage the exterior of the body of a syringe having a back end, as theback end of the syringe body is received by the syringe guide and movedaxially along the guide toward the housing.
 8. A combination of syringeand front loadable power injector for injecting liquid into the body ofan animal at an operating pressure, the combination comprising:a powerinjector having a pressure jacket having a bore therethrough configuredto receive a syringe therein, the jacket having an open front enddimensioned to facilitate the insertion of a syringe, back end first,into the bore and removal of the syringe from the bore, and a pressurerestraining side wall; a removable syringe having a forward portion bywhich the syringe can be held for loading to and unloading from theinjector, the syringe being mountable in the bore through the front endof the jacket and lockable relative to the injector with the forwardportion thereof extending from the front end of the jacket, the syringehaving a pressure restraining front and a tubular body that is outwardlydeformable when liquid at operating pressure is contained therein; andthe pressure jacket being configured to closely surround the tubularbody of the syringe and inhibit the outward deformation thereof at theoperating pressure.
 9. The combination of claim 8 wherein:a removablesyringe includes a contrast medium contained within the fluid cavity.10. A front loadable power injector for injecting liquid into the bodyof an animal at an operating pressure, the injector comprising:a housinghaving a plunger drive ram extendable therefrom and containing a powerdrive energizeable to move the plunger drive ram; a pressure jackethaving a bore therethrough configured to receive a syringe therein, thejacket having an open front end dimensioned to facilitate insertion ofthe syringe into the bore therefrom and removal of the syringe from thebore thereby, and a pressure restraining side wall, the front end of thejacket having substantially no pressure restraining capability, the borehaving a longitudinal axis; a removable syringe mountable in the borethrough the front end of the jacket, the syringe having a hollow body, arestraining front wall and a plunger slidable within the body; and asyringe lock carried in part by the syringe proximate the front wallthereof and in part by the pressure jacket proximate the front endthereof, the lock being operative to releasably form a force restrainingconnection between the syringe front wall and the front end of thepressure jacket to hold the syringe in the pressure jacket when theplunger drive ram advances the plunger within the body and the pressureof the liquid in the cavity reaches the operating pressure.
 11. Theinjector of claim 9 wherein:the removable syringe includes a contrastmedium contained within the fluid cavity.
 12. A front loadable powerinjector for injecting liquid into the body of an animal from adisposable replacement syringe having a fluid cavity therein, a frontend discharge orifice communicating with the cavity and a plungermoveable in the cavity and drivably accessible from an open back of thesyringe, the injector comprising:a housing; a hollow jacket extendingforward from the housing and having an open syringe receiving front end;a drive ram movably supported on the housing and having a front endaxially extendable and retractable therefrom within the jacket; a powerunit carried by the housing and drivably linked to the drive ram; asyringe lock fixed relative to the housing and configured to lock asyringe in the jacket upon specific movement of the syringe relative tothe jacket.
 13. The injector of claim 12 further comprising:a plungercoupling mounted on the front end of the drive ram and operable toaffect a connection between the ram and the plunger of a syringe whenmounted in the jacket upon relative translatory motion therebetween; andlinkage connected between the ram and the jacket to impart relativetranslatory motion therebetween.
 14. The injector of claim 12 furthercomprising:a plunger coupling mounted on the front end of the drive ramand operable to affect a connection between the ram and the plunger of asyringe when mounted in the jacket upon relative translatory motiontherebetween; and linkage connected between the ram and the jacket toimpart relative translatory motion therebetween; and the linkage isoperative to impart the relative translatory motion between the ram andthe jacket in a direction transverse to the direction of axialmoveability of the ram within the jacket.
 15. The injector of claim 12wherein:the syringe lock is operable to lock a syringe to the jacketupon relative rotational movement of the syringe relative to the jacket.16. The injector of claim 15 further comprising:a plunger couplingmounted on the front end of the drive ram and operable to affect aconnection between the ram and a plunger of a syringe when mounted inthe jacket upon relative translatory motion therebetween; linkageconnected between the ram and the jacket to impart relative translatorymotion therebetween; and the linkage is disposed to operate upon therotational motion of the syringe relative to the jacket to impart therelative translatory between the ram and the jacket simultaneously withthe rotation of the syringe relative to the jacket.
 17. A combination ofa disposable syringe and front loaded power injector for injectingliquid into the body of an animal from the disposable syringe having afluid cavity therein, a front end discharge orifice communicating withthe cavity and a plunger moveable in the cavity and drivably accessiblefrom an open back of the syringe, the combination comprising:an injectorhaving:a housing; a hollow jacket extending forward from the housing andhaving an open syringe-receiving front end; a drive ram movablysupported on the housing and having a front end axially extendable andretractable therefrom within the jacket; a power unit carried by thehousing and drivably linked to the drive ram; a plunger coupling mountedon the front end of the drive ram and operable to affect a connectionbetween the ram and the plunger of the syringe when mounted in thejacket upon relative translatory motion between the ram and the plunger;linkage connected between the ram and the jacket to impart relativetranslatory motion therebetween; and a syringe lock carried by thejacket and operable to lock a syringe to the jacket upon the rotationalmotion of the syringe relative to the jacket.
 18. The combination ofclaim 17 wherein:the linkage is disposed to operate upon the rotationalmotion of the syringe relative to the jacket to impart the relativetranslatory between the ram and the jacket simultaneously with therotation of the syringe relative to the jacket; and the syringe isremovably mounted in the jacket through the front end of the jacket andhas locking structure thereon engageable with the syringe lock upon therotation of the syringe relative to the jacket.
 19. The combination ofclaim 17 wherein:the syringe is removably mounted in the jacket throughthe front end of the jacket and has a body having a fluid cavitytherein, fluid media contained in the cavity, and locking structurecarried by the syringe and engageable with the syringe lock.
 20. Thecombination of claim 17 wherein:the syringe is removably mounted in thejacket through the front end of the jacket and has a body having a fluidcavity therein and locking structure carried by the body and engageablewith the syringe lock.
 21. A combination of a disposable syringe andfront loaded power injector for injecting liquid into the body of ananimal from the disposable syringe having a hollow body containing afillable fluid cavity on the interior thereof, a plunger axiallymoveable within the cavity, and a forward portion by which the syringecan be held for loading to and unloading from the injector, thecombination comprising:an injector having:a housing; a syringe guidecarried by the housing having a syringe receiving front end; lockingstructure at least partially carried by the injector and configured tolock the syringe relative to the injector while the forward portion ofthe syringe is being held; a drive ram movably supported on the housingand having a front end extendable and retractable therefrom in an axialpath along the syringe guide; a power unit carried by the housing anddrivably linked to the drive ram; the syringe guide being configuredrelative to the path of the drive ram to maintain the interior of asyringe received by the syringe guide out of contact with the ram whenthe ram is in an extended position along the path.
 22. The combinationof claim 21 wherein:the syringe has fluid media contained in the cavitythereof and cooperating locking structure carried by the body thereofand Iockingly engaged with the locking structure on the injector withthe forward portion of the syringe extending from the front end of theguide.
 23. The combination of claim 21 wherein:the locking structure isfixed to the front end of the guide; and the syringe is removablymounted to the injector with the forward portion thereof locked to thelocking structure.